Homo Erectus
By 1.8 million years ago, some of the early transitional
humans had evolved into a new, fully human species in
Africa. Most paleoanthropologists refer to them as
Homo erectus (literally "upright human"). However, a
few researchers split them into two species--Homo
ergaster (literally "working human") and Homo erectus.
The ergaster fossils were presumably somewhat earlier
and have been found for the most part in Africa. The
erectus discoveries have been found widespread in
Africa, Asia, and Europe. In this tutorial, ergaster and
erectus will be considered one species--Homo erectus.
Homo erectus were very successful in creating cultural
technologies that allowed them to adapt to new
environmental opportunities. They were true pioneers
in developing human culture and in moving out of Africa
to populate tropical and subtropical zones elsewhere in
the Old World. This territorial expansion most likely
began around 1.8-1.7 million years ago, coinciding with
progressively cooler global temperatures. Surprisingly,
however, Homo erectus remained little changed
anatomically until about 800,000-700,000 years ago.
After that time, there apparently were evolutionary
developments in features of the head that would
become characteristic of modern humans. By half a
million years ago, some Homo erectus were able to
move into the seasonally cold temperate zones of Asia
and Europe. This migration was made possible by
greater intelligence and new cultural technologies,
probably including better hunting skills and the ability to
create fire.
The Homo erectus skeletal evidence at the "Peking Man"
site of Zhoukoudian is especially important because it is
from a population of men, women, and children rather
than just a single individual. There was considerable
sexual dimorphism and individual variability. The human
remains were associated with large quantities of animal
bones that apparently were mostly food refuse, though
many of them had been chewed by large carnivores. A
few of the bones had been burned in a way that
suggests cooking. In addition, more than 100,000 stone,
bone, antler, and horn tools were excavated. The cave
was intermittently occupied by late Homo erectus for
around 300,000 years, beginning around 750,000 years
ago.
In 1960, Louis and Mary Leakey found a 1.25 million
year old Homo erectus partial cranium at Olduvai
Gorge. Subsequently, more Homo erectus fossils were
discovered there and at other sites in East, South, and
Northwest Africa. The oldest known Homo erectus date
to nearly 2 million years ago in East Africa. This strongly
suggests that Homo erectus originated there. In 1984,
Richard Leakey's team working at Nariokotome on the
western side of Lake Turkana found a nearly complete
Homo erectus skeleton of a 12 year old boy dating to 1.6
million years ago. It was named the "Turkana Boy."
Three surprisingly early Homo erectus skulls were found
during the 1990's on the fringes of Eastern Europe at
Dmanisi in the Republic of Georgia. They date to 1.75
million years ago and look very much like the earliest
Homo erectus from Africa--i.e., those that have been
classified by some researchers as Homo ergaster. This
discovery lends credence to the 1.8 and 1.6 million year
old dates for Homo erectus from Java and to an early
rather than late Homo erectus expansion out of Africa.
Homo erectus-like bones were also discovered during
the 1990's from several other sites in Western Europe
and Africa that date 800,000-400,000 years ago. This
partly reflects the fact that the picture of human
evolution looks somewhat dissimilar in different regions
of the World. It is now becoming clear that our
evolution was not as straight forward as it once was
commonly thought. Humans in some areas lagged
behind.
Anatomy
Below the neck, Homo erectus were anatomically much
like modern humans. Their arm and leg bones were
essentially the same as modern people in shape and
relative proportions. This strongly supports the view
that they were equal to us in their ability to walk and
run bipedally. However, their leg bones were apparently
denser than ours. This may be partly a result of
developmental adjustment differences. Unlike us, these
early humans did not spend much of their lives sitting
behind desks or on a sofa watching TV. They were
probably much more active throughout the day seeking
food.
Their legs would have made Homo erectus efficient long
distance runners like modern humans. It has been
suggested that this capability would have allowed them
to run down small and even medium size game animals
on the savannas of Africa. If this was the case, it is also
likely that they were largely hairless by this time. Bodies
with little hair are more efficient at remaining cool via
the evaporation of sweat during times of heavy
exertion. Most other mammals primarily cool their
bodies by panting. Because panting is less able to keep
running animals from over heating, human hunters have
a decisive advantage when chasing them over long
distances.
It also has been suggested that the pelvis in early Homo
erectus may have been a bit narrower than in modern
humans, which would require the infant brain to be
smaller at birth and to then undergo considerable
growth in childhood. However, we must be careful to
not make too much of these differences because the
number of existing specimens is low and there were
minor regional variations as well. This becomes
apparent especially when comparing Homo erectus from
Asia and Africa.
With the evolution of Homo erectus, there was a
significant increase in body size compared to earlier
hominids. Past estimates of Homo erectus stature
frequently were in the 5-5½ feet (1.5-1.7 m.) range for
adult males and around 100-110 pounds (45-50 kg.).
The discovery of the "Turkana Boy" in 1984 brought this
into question. This is not only the most complete
specimen of this species so far discovered, but it is one
of the earliest. The boy was only about 8-12 years old
when he died but already 5 feet 3 inches (1.6 m.) tall. If
he had lived to adulthood, he very likely would have
grown to 6 feet (1.8 m.). As the number of nearly
complete Homo erectus skeletons increases in the
future, a clearer understanding of the range of their
stature and body shape will likely emerge.
Homo erectus heads were strikingly different from ours
in shape. They had relatively strong muscles on the back
of their necks. Their foreheads were shallow, sloping
back from very prominent bony brow ridges (i.e.,
supraorbital tori ). Compared to modern humans, the
Homo erectus brain case was more elongated from front
to back and less spherical. As a consequence, the frontal
and temporal lobes of their brains were narrower,
suggesting that they would have had somewhat lower
mental ability.